Carotenoid is a kind of pigment with the largest and widest presences in nature. Carotenoid compounds are widely used for pigmentations of foods, cosmetics and pharmaceuticals, etc. Recently studies have shown that carotenoids have better curative effects on preventing, postponing and curing certain diseases as well as improving immunities.
β-carotene is an important carotenoid, its chemical formula is C40H56 and its molecular weight is 536.88, and is formed by bonding the double bonds of four isoprenes, mainly has four forms of all-trans, 9-cis-form, 13-cis-form and 15-cis-form. The molecular structural formula of β-carotene is as follows:

There is a β-ionine ring at each end of molecular structure thereof, the β-ionine could exist in the form of isomer form, substitutional form and opening-ring form.
β-carotene has important physiological functions and may serve as a precursor of vitamin A, and is a nutrition food fortifier with Class A recognized by Joint Expert Committee on Food Additives of United Nations FAO and World Health Organization. Studies have shown that β-carotene as the precursor of vitamin A has effects on antioxidation, influence reproduction and thyroid function etc. Many double bonds in a β-carotene molecule are readily oxidized so as to play a role on antioxidation accordingly and protect bodies from being damaged in the presence of light, heat, oxygen and more activities free radical ions. In addition, studies also have shown that β-carotene can improve immunities, enhance anticancer abilities, promote connections and communications between cells, and have anti-nicotine effects and so on.
β-carotene derives from total synthesis and nature. Recently people are in favor of natural β-carotene because β-carotene obtained by total synthesis may exist some chemical intermediate impurities. There are three methods of producing natural β-carotene including extracting from natural plants, culturing salina and producing by microorganism fermentation. A certain amount of natural β-carotene may be obtained by extraction and separation from vegetables containing a trace of β-carotene such as carrot and so on. But deficiencies of the method are obviously a lot of material costs and low production. The second method of obtaining β-carotene is to culture a large area of salina such as Dunaliella salina and then solvent extraction. But the culturing salina is strictly restricted by external environmental conditions. It makes production scales difficult to expand and meet market demands. The third method of obtaining β-carotene is to microorganism fermentation. But the method is not restricted by environmental conditions, with high yields and easy to achieve industrialization. More and more research institutes and manufacturers devote themselves to the researches. The microbial strains for producing natural β-carotene at home and abroad are mainly Bacillus ramosus, Rhodothece glutinis, etc. Popular strains are filamentous fungus such as Blakeslea trispora, Neurospora sitophila, etc., wherein the most popular strain is Blakeslea trispora. 
Producing natural β-carotene by using Blakeslea trispora is to mix and fermente two kinds strains thereof such as strains (+) and (−), The method is in detail described in PCT application of WO 00/77234, Caglioti L. et al. (1966). Recently researches mainly pay attention to how to change fermentation conditions or add precursor substances to increase fermentation unit and how to effectively separate and obtain high quality pure β-carotenes from fermented mycelia. More patent documents have reported these aspects and shown many improving measures. But there are many technical deficiencies in these measures or production processes, for example, higher costs of producing due to low fermentation units and then no beneficial for industrial production; or complicated processes of extraction and purification of β-carotene, or difficultly extracted intracellular products in fermentation; or food safety risks due to greater toxicity organic solvents used in extraction and purification; or low content of β-carotene due to more impurities.
U.S. Pat. No. 3,752,740 produces natural β-carotene by using Blakeslea trispora fermentation by adding 7.5% citric acid into medium. But the fermentation unit in the final fermentation liquid is too low to be suitable for industrial production.
U.S. Pat. No. 7,252,965 discloses a selected and optimized Blakeslea trispora, and increases yields of β-carotene in the fermentation liquid by measures of adding precursor substance β-ionine and increasing dissolved oxygen constrainedly during fermentation courses, and β-carotene unit in the final fermentation liquid can achieve to 9 g/L. The process does not relate to any courses of extracting β-carotene from mycelia.
CN 1,193,048A provides processes of preparing β-carotene by culturing filamentous fungus to ferment in a fermenter. The process comprises Level 1 strain culture and Level 2 strain culture as well as fermentation course. The PDA medium thereof comprises glucose, potato and agar medium. The medium of Level 2 strain culture and fermentation culture comprises starch, glucose, starch, corn syrup, dipotassium hydrogen phosphate, magnesium sulfate, thiamine hydrochloride and vegetable oil, etc. The process improves dissolved oxygen by improvements of equipment, but the fermentation unit is low in the fermentation liquid, and large quantities of greater toxicity organic solvent such as N-hexane, etc. is used in the extraction.
EP 1,306,444 B1 relates to a method of producing β-carotene by using Blakeslea trispora to ferment and extracting β-carotene from mycelia. It needs to add lecithin and adjust pH of fermentation liquid stage-by-stage during fermentation process. But there are many steps in the process of extraction and purification of β-carotene, such as refining filtrating mycelia by alcohols, drying and pulverizing mycelia, extracting by organic solvents, concentrating organic solvents after extraction, crystallizing by adding alcohols solvent, filtrating and drying, etc. The processes of extraction and purification of β-carotene are very complicated including drying and pulverizing steps for at least three times, drying and pulverizing wet mycelia after refining, drying and pulverizing pure β-carotene after extraction, and drying the residua of mycelia after the extraction of β-carotene being completed. Likewise, it certainly involves three times transfer processes of powder materials and will bring series of additional requirements for equipments and techniques in the industrial production, and twice heating and drying processes are very bad for unstable substances when β-carotene heated. It certainly makes yields of final product decrease. In addition, pulverizing processes of mycelia increases working procedures. Besides fine powders in the pulverizing process is also bad for occupational health.
In brief, there are such deficiencies as complicated processes and inadequacy for industrial production in the prior art. So it is necessary to find a method of producing β-carotene with high yield via Blakeslea trispora and expediently extracting β-carotene produced by fermentation in spores by an effective way. The present invention provides a method of obtaining natural β-carotene with high yields by culturing Blakeslea trispora. 